Fionn loved to hunt with his two great hounds Bran and Sgeolan who came from the realms of the Otherworld. One day when they were hunting near his home Allmu of the White Walls, they set after a hind that ran so swiftly that not even Bran and Sgeolan could catch her and it seemed to Fionn that the hind was racing directly towards Allmu in search of sanctuary. Sure enough as Fionn approached his home Bran and Sgeolan who were ahead barked excitedly that they had cornered their quarry, but when Fionn got close enough he could see that instead of ripping the hind in pieces they were instead licking her and fawning upon her as if she were a long lost sister. Then Fionn knew it was no ordinary hind and called the rest of the Fianna and their dogs off. He took the hind into his home with Bran and Sgeolan following behind.
That night the hind sat at Fionn's feet and when he went to bed she came and lay beside him, and when he awoke later on he found a beautiful woman lying beside him with big lustrous eyes just like the eyes of the hind. Then she told Fionn her story. She was one of the Faery people, the Lordly Ones of Tír na nÓg and that one of her people had desired her although she always refused him and in his wrath he had struck her with his hazel rod and turned her into a hind. She asked Fionn could she stay with him and he asked her name and she told him it was Sabha. He said that he would allow her to stay with him if she would agree to become his wife. So she agreed and they drank the bride-cup together and were happy for a year in which Fionn almost forgot about hunting or going very far from the walls of Allmu.
This contentment could not last forever as the Fianna had a job to protect Ireland's coastline from invaders and one day they were all called into action as enemies were sighted off the shore. Fionn told Sabha to remain at Allmu and talk to only the trusted people of the fortress.
Fionn went out with the Fianna and fought bravely against the invaders and came back victorious and all the while searching the ramparts of the fortress for a glimpse of Sabha. When he could not see her a feeling of dread overcame him and he felt sick in his stomach, and he rushed in to his steward and demanded to know where Sabha was. The steward told him that only two days after he had left for battle a man rode into the courtyard that looked exactly like Fionn and even had two hounds that looked like Bran and Sgeolan and when Sabha saw him she ran to him with a cry of joy thinking that it was Fionn himself, but as soon as she got up close to the man he hit her with a hazel wand and she became a hind again and in that moment the two hounds vanished away and the man changed his appearance into a strange dark figure who led the hind away.
Then Fionn knew that it was the Faery Lord who had previously been a suitor to Sabha who had led her away and he believed he would never see her again. He set out to search for her just in case and combed every part of the hills and vales where he first met her but it was all in vain and he decided to return to the leadership of the Fianna which he had allowed to lapse while he searched for Sabha.
Fionn was broken-hearted and seven years went by and once again he was out hunting with his hounds Bran and Sgeolan and this time they discovered a strange sight - a little naked boy wandering about on the hill of Benbulben and although Fionn spoke to him he knew no words of human speech.
So Fionn took him to Allmu and cared for him and taught him to speak until the day came when he could tell his story. For as long as he could remember he had lived in a cave in the hills with a hind for company. Then one day a dark man had come who wanted the hind to go with him and when she refused he struck her with his wand and after that she went though always looking back to where he stood watching, and although he wished to run after her he could not even move a finger until at last he heard the cry of Fionn's hounds and was discovered by Bran and Sgeolan.
Then Fionn knew that this was his own child and that of Sabha's and he named him Oisín which means 'little deer' and he thought he might try once more to see if he could find Sabha so he went to the mound of Slieve Gallion in Armagh where Cuillen the Smith of the sidhe lived with his two daughters Áine and Milucra.
Now unknown to Fionn, Áine had fallen in love with him years ago and when he showed no signs of returning her feelings as he only had eyes for Sabha, she was furious and now he came riding by her home she decided to get revenge.
So when Fionn was nearing Slieve Gallion, he came upon a small dark lough in the shelter of the hills and sitting beside it was a beautiful woman crying bitterly. 'Why are you crying?' asked Fionn, and she replied that she had lost a red-gold ring that was a present from her lover and then she put a geis on Fionn (an obligation which he could not refuse), to search the lough until he had recovered the ring. So Fionn dived into the lake and he swam the length and breadth of it three times before he finally found the ring. When he swam to the bank and stretched out his hand to give her the ring, she snatched it from him and with a high, strange laugh she leapt into the water and was gone. When Fionn climbed out of the lough the moment his foot touched the earth all his youthfulness drained out of him and he lay on the ground like a feeble old man scarcely able to move. Then he was seized with fright and he put his thumb in his mouth to see if his divining power was also gone but luckily that remained and he was able to find out who it was that had done this to him and that there was not a lot he could do to change things.
He remained by the lough growing weaker daily until at last the Fianna came searching for him, and seeing the old man at the lake they asked him had he seen a bright and fair man in his youthful prime riding by, and he answered that he had and it was none other than himself and he told them all the story of what had happened to him.
Then Caoilte Mac Ronan suggested that they call on Cuillen the master of the Faery mound and see if they could get any recompense from him. They all agreed and went immediately to the sidhe of Cuillen and began to dig and root at the hill, they did this for three days and nights and there was a mighty big chunk taken out of the side of the hill when at last Cuillen himself appeared carrying a golden cup in his hands, and coldly he told Fionn to drink from it. When he did he was immediately restored to health except for his hair which remained ashen grey in colour and Cuillen was nowhere to be seen. Fionn decided that it was doubtful he would get anything else from Cuillen and so he left the Faery mound and returned to his home and at least he had Oisín to compensate in part for the loss of Sabha for he never saw her again at least not while he was alive.